The present invention relates to a system for automatically providing interconnections among a plurality of telephone lines serving a subscriber station and, in particular, for providing a means whereby a subscriber can utilize one or more of his lines when he is not physically present at the subscriber station.
A number of prior art systems are available which provide specialized remote control over a telephone line serving a subscriber station. Some such systems permit control and utilization of the telephone line serving a subscriber station from any remote telephone. Two prior art systems are respectively disclosed in U.S. Pat. No. 3,689,702 issued to T. E. McCay on Sept. 5, 1972 and U.S. Pat. No. 3,704,346 issued to L. M. Smith et al. on Nov. 28, 1972.
The McCay system permits an outgoing line to be controlled by a caller calling in on an incoming line, and permits the outgoing line to be repeatedly reset for dialing out repeated calls thereon without the caller having to hang up his telephone. Thus, if a subscriber has a Wide Area Telephone Service (WATS) line, foreign exchange (FX) line or tie line at his office, he can repeatedly utilize that line from any location for the price of a single telephone call to his office. But the McCay system provides no effective means for the subscriber to utilize his office phone from a remote location to make local calls in the area of his office because his system is essentially one-way and provides no means for controlling the "incoming" line from the "outgoing" line.
Furthermore, both of the above-mentioned prior art systems provide for the interconnection of only two subscriber lines, one incoming and one outgoing. If the subscriber has a long distance line, that line is made the outgoing line since it is the one he will usually wish to utilize from a remote location. Outgoing calls can be made on only one line and incoming control signals can only be transmitted over one line. The user does not have the option of using the system to make either long distance or local calls.
Additionally, since only a two-line interconnection is possible in the prior art systems, three-party conference calls cannot be established on those systems. While conference call circuits are, in general, well-known in the telephone art, all conference calls using such prior art circuits must either be established by an operator located at a central location, or require the person placing the conference call to be calling from a specially equipped central office or PBX. The prior art does not provide any means for permitting a user to call into a central station from any remote telephone and set up a conference call without the aid of an operator at the central station.
In utilizing the Smith et al. system in its call-through mode (FIG. 2), dialing signals, whether tone type or pulse type, are decoded and control a dial-out mechanism which pulses the outgoing line to simulate dialing thereon. This is necessary because dialing signals cannot pass through the smith et al. repeater amplifier 31 while dial tone from the outgoing is present. Alternatively, the Smith et al. system could interrupt the dial tone and have the incoming callar wait until the dial tone ceases before dialing out his call, but this is an awkward and unnatural mode of operation. The prior art system provides no convenient means for the user to directly transmit his dialing signals from the incoming line to the outgoing line upon hearing dial tone.
In the above-mentioned prior art systems, if a caller finds the system busy, there is no provision for his notifying the users of the system that there is a caller waiting. While caller-waiting indication means are, in general, known in telephone systems, most indicate that someone is waiting for connection to a specific called line, rather than waiting to use an interconnection facility. Such prior art devices provide for a caller-waiting indication to be automatically generated when an incoming caller receives a busy signal. The caller-waiting indication will be impressed on the interconnection regardless of the identity of the waiting caller. There is no caller selectability of the caller-waiting indication in such systems. This can be quite bothersome when, for example, an executive's telephone conversations are continually being interrupted by caller-waiting indications as a result of subordinates' attempts to reach him.
Furthermore, while the McCay system provides for line-retention, i.e., the dialing of repeated calls on the outgoing line by the user without hanging up his telephone, this feature is available only with the use of tone type dialing signals. Thus, the location from which the caller is calling must have a standard tone dialing telephone or the caller must carry with him a special tone encoder which simulates the tone dialing signals. This limitation constitutes a considerable inconvenience.
The McCay system also provides for the user of a security access code which must be dialed in by the caller in order to effect the interconnection of the incoming and outgoing lines. McCay discloses that his access code can be changed from time to time, but does not disclose how this change is effected. No convenient means is disclosed in the prior art for permitting the access code to be simply and easily changed at will, but only by authorized personnel, nor does the prior art disclose means for selectively bypassing the security code mode of operation.